The heat exchangers of a widely prevailed type are structured as follows. Planar portions of a single flat tube are horizontally disposed while fins are respectively interposed between given two adjacent planar portions (see Japan Examined Utility Application Publication No. 63-006632). Japan Examined Utility Model Application Publication No. S63-006632 describes a heat exchanger that each of the fins includes a plurality of protruding portions protruded to the downstream of airflow and each of the protruding portions includes a cutout. Condensed dew, generated in the heat exchanger, gathers in the downstream of airflow and drops downwards through the cutouts. However, the condensed dew normally drops through the cutouts when becoming larger to naturally drop due to its weight. Otherwise, the condensed dew is accumulated in the heat exchanger. In this case, the condensed dew blocks ventilation and accordingly deteriorates heat exchange performance of the heat exchanger. In view of the above, the applicant of the present invention developed a heat exchanger having an enhanced drainage performance with respect to condensed dew. Specifically, the heat exchanger has a structure that the fins are respectively interposed between given two adjacent planar portions while being protruded from the edges of the planar portions. Accordingly, condensed dew flows downwards through the protruded portions of the fins (see Japan Laid-open Patent Application publication No. 2008-101847)
There have been further increasing demands for reduction in size of the heat exchangers. However, reduction in size of the heat exchangers may possibly deteriorate drainage performance of the heat exchangers with respect to condensed dew. In response, there have been demands for further enhancement in drainage performance of the heat exchangers.